Oil-based ink composition for ballpoint pen and ball-point pen using oil-based ink

ABSTRACT

An oil-based ink composition for a ball-point pen that enables suppression of a blobbing phenomenon by controlling the internal cohesion force of an ink is provided; An oil-based ink composition for a ball-point pen at least comprising a colorant, a resin, and from 0.01 to 1.5% by weight of a high polymerization degree polybutyl vinylal with a polymerization degree of 900 (theoretical molecular weight of 60,000) or more and comprising, as a main solvent, a solvent selected from alcohols, polyhydric alcohols, and glycol ethers with a vapor pressure at 25° C. of 0.001 mmHg or higher by 50% or more for the entire solvent. Further, an oil-based ink composition for use in a ball-point pen having a smooth feel in writing, and excellent in the improvement for the fastness and the dispersion stability of the coloring pigment is provided; an oil-based ink composition for use in a ball-point pen containing, as a main solvent, a solvent of the chemical structural formula (1)  
                 
 
where R 1 , R 2 , and R 3  each represents independently H or CH 3 .

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an oil-based ink composition for aball-point pen and an oil-based ball-point pen. More specifically, itrelates to an oil-based ink composition for a ball-point pen having softand smooth feel on writing and rapid penetration of the ink to a writingpaper surface, and able to suppress point seepage (deposition blobbing)of the ink at a pen tip during writing and an accompanying dripping ofthe ink onto the paper surface (drawn line blobbing) as much aspossible. It also relates to an oil-based ink composition for aball-point pen having a smooth feel on writing, and excellent in animprovement of fastness, a coloring property and the dispersionstability of a pigment. It further relates to an oil-based ball-pointpen using the oil-based ink composition and having aback-flow-preventive mechanism mounted therein.

BACKGROUND ART

Heretofore, in oil-based ball-point pens, for suppressing a so-calledsagging phenomenon in which an ink leaks from the top end of a tip,point seepage at the tip or blobbing phenomenon of contaminating thepaper surface due to a simple structure thereof, problems were solved bythe approach of controlling the viscosity of the ink to about 10,000mPa·s, restricting the ink discharge mechanism in view of the structuraldesign such as the inner diameter of a ink containing tube, clearance atthe pen tip, etc., adding inorganic filler particles to the ink therebyproviding thixotropy, or adding a certain polymer to give an effect onthe ink discharge. However, as mixed solvents comprising components suchas less volatiling aromatic type glycol ether and aromatic type alcoholare usually used for the ink solvent, no remarkable progress has beenmade other than the procedures described above.

In view of the above, an object in the first aspect of the invention isto provide an ink composition for a ball-point pen that enablessuppression of the blobbing phenomenon by controlling the volatility ofthe ink solvent to prevent excessive drying on the ball surface andsuppressing the blobbing phenomenon by controlling the internal cohesionforce of the ink.

Further, in the commercially available oil-based ball-point pensdescribed above, the solvent comprises a mixture of 2-phenoxy ethanoland benzyl alcohol, and an oil-based ball-point pen using, as the mainsolvent, a solvent represented by the chemical structural formula

where R¹, R², and R³ each represents independently H or CH₃ has not yetbeen commercially available.

While seeking a smooth writing feel, rapid ink penetration to thewriting surface, a good drying property at the pen tip, etc., thepresent inventor has studied ink compositions using, as a main solvent,a solvent of chemical structural formula (1) (refer to Japanese PatentApplication No. Hei 12-232004 which was not laid-open at the time offiling Japanese. Patent Application No. 2002-275807 as the basis forclaiming the priority of the present application).

Further, in the conventional oil-based ball-point pens, as it isdifficult to use a pigment in the oil-based ball-point pen, lightfastness was usually ensured by using, for example, a metal-containingdye in order to enhance the light fastness. However, a pigment isexcellent in view of the fastness.

Further, in the conventional oil-based ball-point pens, as a highviscosity ink is used, it has not been adopted, to provide back-flowingstructure, an ink follower for preventing back flow, or providing aback-flow-preventive mechanism at a joint portion connecting a tip andan ink containing tube in order to prevent back flow.

The present inventor had reached that idea that, in the oil-basedball-point pen using the ink composition using the solvent of thechemical structural formula (1) as a main solvent, the flowability ofthe solvent is high and air tends to intrude from the pen tip and causedisadvantages it is necessary to mount a back-flow-preventive mechanism.Further, with the intention of using a pigment for light fastness, theinventor has made a study to provide an oil-based ink compositionfavorable in the fastness, coloring property and dispersion stability ofthe pigment, in an oil-based ball-point pen that holds an inkcomposition using the solvent of the chemical structural formula (1) asa main solvent, and a back-flow-preventive mechanism.

In the second aspect, the invention is intended to provide an oil-basedink composition for use in a ball-point pen having smooth feel ofwriting, and excellent in the improvement of the fastness, the coloringproperty and the dispersion stability of the pigment and having aback-flow-preventive mechanism therein, different from the conventionalmethod, and an oil-based ball-point pen having a back-flow-preventivemechanism and using the oil-based ink composition described above.

DISCLOSURE OF THE INVENTION

To attain the objects described above, it has been found that theoil-based ink composition for a ball-point pen according to theinvention can solve the problems by the features shown below and theinvention has been accomplished.

[1] An oil-based ink composition for a ball-point pen comprising atleast a colorant and a resin, as well as a solvent selected fromalcohols, polyhydric alcohols and glycol ethers each having a vaporpressure at 25° C. of 0.001 mmHg or higher as a main solvent occupying50% or more of the entire solvent, and satisfying at least one of thefollowing (a) and (b):

-   -   (a) comprising from 0.01 to 1.5% by weight of a high        polymerization degree polybutyl vinylal with a polymerization        degree of 900 (theoretical molecular weight of 60,000) or more,        and    -   (b) comprising a pigment as the colorant and polybutyl vinylal        as a dispersant, said main solvent being a solvent represented        by the following chemical structural formula (1):        where R¹, R², and R³ each represents independently H or CH₃.

[2] The oil-based ink composition for a ball-point pen according to [1]described above, wherein, in a case of (a) described above, the glycolether is represented by the following chemical structural formula (1):

where R¹, R², and R³ each represents independently H or CH₃,

[3] The oil-based ink composition for a ball-point pen according to [1]or [2] described above, wherein the colorant is a pigment or a pigmentand a dye used in combination.

[4] The oil-based ink composition for a ball-point pen according to anyone of [1] to [3] described above, wherein, in the case of (a) describedabove, polyvinyl butyral with a polymerization degree of 900(theoretical molecular weight of 60,000) or less is further used as apigment dispersant.

[5] The oil-based ink composition for a ball-point pen according to [4]described above, wherein polyvinyl butyral with a polymerization degreeof 200 or more and 500 or less (theoretical molecular weight of from10,000 to 30,000) is used as said pigment dispersant.

[6] The oil-based ink composition for use in a ball-point pen accordingto any one of [1] to [5] described above, wherein a neutralizationproduct of a phosphate ester is contained as an additive.

[7] The oil-based ink composition for use in a ball-point pen accordingto [1] above, wherein in the case of (b) described above, the polyvinylbutyral has an average molecular weight of from 10,000 to 30,000.

[8] The oil-based ink composition for use in a ball-point pen accordingto [1] or [7] described above, which has an ink viscosity at 25° C. offrom 500 to 3,000 mPa·s.

[9] The oil-based ball-point pen comprising said oil-based inkcomposition for a ball-point pen as set forth in any one of [1] to [8],and a back-flow-preventive mechanism provided to a joint portionconnecting a tip and an ink containing tube.

[10] The oil-based ball-point pen according to [9] described above,wherein an ink follower is further provided to an ink rear end portionof an ink containing tube to prevent ink evaporation and back flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view showing an example of aball-point pen that mounts a back-flow-preventive mechanism therein.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

<First Aspect of the Invention (Condition (a))>

As the main solvent (50% by weight or more of the entire solvent) usedfor the composition of the invention, a solvent selected from alcohols,polyhydric alcohols, and glycol ethers with a vapor pressure at 25° C.of 0.001 mmHg or higher is used. The specified solvent with high vaporpressure as described above gives a smooth writing feel and rapid inkpenetration to the writing surface. The ink-based ink composition for aball-point pen of the invention has been developed with an aim ofsolving the problem inherent to the case of using a specific solventwith such a high vapor pressure. The main solvent means that it is 50%by weight or more of the entire solvent and it can, optionally, be 70%by weight or more, further, 80% by weight or more, and, particularly,90% by weight or more.

Specifically, alcohols are aliphatic alcohols with 2 or more of carbonatoms and include, for example, ethanol, n-propanol, isopropanol,n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol,sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methylamylalcohol, 2-ethyl butanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol,2-octanol, 2-ethylhexanol, 3,5,5-trimethyl hexanol, nonanol, n-decanol,undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol,heptadecanol, cyclohexanol, 2-methylcyclohexanol, benzyl alcohol andvarious other higher alcohols.

Further, the polyhydric alcohols include those polyhydric alcoholshaving two or more carbon atoms and two or more hydroxy groups in themolecule such as ethylene glycol, diethylene glycol,3-methyl-1,3-butanediol, triethylene glycol, dipropylene glycol,1,3-propane glycol, 1,3-butanediol, 1,5-pentanediol, hexylene glycol,and octylene glycol.

The glycol ethers include, for example, methyl isopropyl ether, ethylether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butylether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether,ethylene glycol monophenyl ether, ethylene glycol mono-2-ethyl butylether, ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycol monobutylether, triethylene glycol monobutyl ether, tetraethylene glycolmonobutyl ether, 3-methyl-3-methoxy-1-butanol, 3-methoxy-1-butanol,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monopropyl ether, propylene glycol monobutyl ether,propylene glycol phenyl ether, propylene glycol tertiary butyl ether,dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether,dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether,tripropylene glycol monomethyl ether, tripropylene glycol monobutylether, and tetrapropylene glycol monobutyl ether.

Particularly preferred are those solvents represented by the chemicalstructural formula (1) and include, for example, 1,3-butane diol,3-methoxy-1-butanol, and 3-methyl-3-methoxy-1-butanol.

Among the solvents described above, particularly preferred are glycolethers of 2 to 7 carbon atoms the effect of which is, particularly,recognizable easily. Further, with the view point of safety, oraltoxicity, etc., organic solvents other than ethylene glycol derivatives,etc. are preferably used.

Further, in addition to the solvents described above, the solvents shownbelow can also be added. In this case, other solvents are preferablyadded, in a case of adding a mixture of a phosphate ester and an aminetype compound to be described later, within such a range as nothindering the solubility therewith, and the evaporation function.

Examples of them are polyhydric alcohol derivatives and also includesorbitan fatty acid type, polyglycerine higher fatty acid type, sucrosefatty acid type and propylene glycol fatty acid type derivatives.

The ester solvents include, for example, various esters such aspropylene glycol methyl ether acetate, propylene glycol diacetate,3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate,ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate,isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate,isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate,propyl propionate, isobutyl propionate, isoamyl propionate, methylbutyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethylisobutyrate, propyl isobutyrate, methyl valerate, ethyl valerate, propylvalerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate,methyl trimethyl acetate, ethyl trimethyl acetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methylcaprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyllaurate, methyl oleate, ethyl oleate, triglyceride caprylate, tributylacetate citrate, octyl oxystearate, propylene glycol monolicinorate,methyl 2-hydroxy isobutyrate, 3-methoxybutyl acetate.

Further, diether or diester solvents not having hydroxyl groups in themolecule specifically include, for example, ethylene glycol diethylether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether,diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, anddipropylene glycol dimethyl ether.

The colorant used in the oil-based ink for a ball-point pen of thepresent invention is preferably used, although not restricted, in theform of a pigment or a pigment and a dye used in combination. Use of thepigment can provide excellent fastness. As the pigment, carbon black,and organic pigments such as phthalocyanine type, azo type includinginsoluble azo type such as monoazo, disazo, condensed azo and chelateazo type and soluble azo type such as less soluble azo type and solubleazo type, quinacridone type, diketopyrrolopyrrole type, threne type,dioxadine type and isoindolinone type can be used.

Particularly, for the carbon black, those with a specific surface areaas small as possible should be used. Those having a value of 100 m²/g orless as measured by the BET method are preferred. Specifically, theyinclude carbon black manufactured by Mitsubishi Kasei such as #33, #32,#30, #25, and CF9, carbon black manufactured by Cabot Co. such as REGAL(400R, 500R, 330R, 300R), ELFTEX (8, 12), and STERLING R, carbon blackmanufactured by Degussa Co. such as Printex (45, 40, 300, 30, 3, 35, 25,200, A, G), and SB (250, 200) and carbon black manufactured by ColombianCo. such as RAVEN (1040, 1035, 1020, 1000, 890, 890H, 850, 500, 450,420, 410, H20, 22, 16, 14).

Further, as the pigment, those less soluble in the organic solvent usedand having an average grain size after dispersion of 30 nm to 700 nm arepreferred. For the blending amount of the pigment, they can be blendedoptionally, within a range from 0.5 to 25% by weight and, preferably,from 0.5 to 20% by weight based on the entire amount of the inkcomposition.

The pigments usable herein can be used alone or as a mixture of two ormore of them. Further, also, a dispersion using an inorganic pigment,dye, etc. can also be added optionally within such an extent as notgiving undesired effects on the dispersion stability. Use of the dye canprovide excellent coloring property. Further, they also include resinemulsions obtained by polymerizing styrene, acrylic acid, acrylateester, methacrylic acid, methacrylate ester, acrylonitrile and olefinicmonomer, hollow resin emulsions which swell in the ink into theindefinite form, or organic multi-color pigments comprising dyed resinparticles obtained by dying the emulsion per se with a colorant.

In a case where the coloring material used in the invention is apigment, various methods known so far can be used for preparing apigment-dispersed ink composition. For example, it can be obtainedeasily by blending each of the ingredients, and then stirring undermixing by a stirrer such as a dissolver, or by mixing and pulverizing bya ball mill, roll mill, beads mill, sand mill, pin mill, etc. and thenremoving coarse particles, undissolved matters and intruded solidmatters of the pigments by centrifugal separation or filtration.

As the dyes used in combination with the pigment described above, any ofthem can be used with no particular restriction so long as it does notdestroy the dispersion system. For the dyes, any of direct dyes, acidicdyes, basic dyes, mordant dyes, acidic mordant dyes, spirit solubledyes, azoic dyes, sulfide/sulfide vat dyes, vat dyes, dispersion dyes,oil soluble dyes, food dyes, metal complex salt dyes, which are used forusual dye ink compositions or organic and inorganic dyes which are usedfor usual pigment ink compositions can be used. The blending amount isselected within a range from 1 to 50% by weight based on the entireamount of the composition.

Resins are used for the oil-based ink composition for a ball-point penof the present invention. The resins are used in the oil-based inkcomposition for controlling the viscosity or improving the abrasionproperty at the pen tip. Further, in a case of using the pigment, it isused also as a dispersant therefor. Such resins include those resinstypically represented, for example, by ketone resin, styrene resin,styrene-acryl resin, terpene phenol resin, rosin modified maleic acidresin, rosin phenol resin, alkyl phenol resin, phenolic resin,styrene-maleic acid resin, rosin type resin, acrylic resin, ureaaldehydel type resin, maleic acid type resin, cyclohexanone type resin,polyvinyl butyral, and polyvinyl pyrrolidone.

The blending amount of the resin is, preferably, from 1 to 30% by weightand, more preferably, from 1 to 20% by weight. In a case where theblending amount is less than 1% by weight, this makes it difficult forthe control of the viscosity and abrasion at the pen tip. In a casewhere it exceeds 30% by weight, raw materials other than the resincannot be blended or it gives an undesired effect on the feel ofwriting.

In a case of using the pigment as the coloring material for the inkcomposition of the invention, as the dispersants to be used, thosecapable of dispersing the pigments can be selected from the resinsdescribed above and used, and it may be an activating agent or anoligomer, irrespective of the type thereof so long as it can suffice thepurpose. Specific dispersant can include, for example, polyvinylalcohol, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl ether,styrene-maleic acid copolymer, ketone resin, hydroxy ethylcellulose orderivatives thereof, synthetic resins, such as styrene-acrylic acidcopolymer, PO/EO (propyrene oxide/ethylene oxide) adducts, and aminetype oligomers of polyesters. However, polyvinyl butyral is particularlyused suitably herein and polyvinyl butyral of a theoretical molecularweight particularly of from 10,000 to 30,000 with a polymerizationdegree of 200 or more and 500 or less can be used suitably. The additionamount is different depending on the characteristics and the additionamount of the pigment that is used within a range from 0.01 to 10% byweight.

Further, in the oil-based ink composition for a ball-point pen of thepresent invention, a high polymerization degree polyvinyl butyral with apolymerization degree of 900 (theoretical molecular amount: 60,000) ormore is essentially used. This is a raw material for controlling theinternal cohesion force of the ink and the addition thereof has aneffect of withdrawing or collecting blobbing that occurs due toexcessive ink during transfer by the internal cohesion force also to anink of low viscosity at 500 to 3,000 mPa-s containing the colorant andthe resin. The polymerization degree of the high polymerization degreepolyvinyl butyral that provides such effect is 900 or more and theeffect is not shown at all in a case where it is less than the degreedescribed above. The polymerization degree is, preferably, 1300 or moreand, more preferably, 1500 or more. Further, it is also possible to usethose with different polymerization degrees in combination. In the inkcomposition of the present invention, the addition amount of the highpolymerization degree polybutyl vinylal should be an extremely smallamount as 0.01 to 1.5% by weight based on the ink composition. Theeffect of withdrawing or collecting the excessive ink relative to theblobbing phenomenon described above is not provided in a case where theaddition amount is less than 0.01% by weight. On the other hand, when itis higher than 1.5% by weight, the viscosity increases excessively togive undesired effects on the raw materials. Since formation of theinternal cohesion force varies depending on the solvent used, the degreefor the reduction of the blobbing phenomenon may sometimes be changed bythe selection of an auxiliary solvent depending on the main solvent bycontrolling the dissolved state thereof.

The polyvinyl butyral used in this aspect in the present inventionincludes, for example, S-LEC B series manufactured by Sekisui ChemicalCo. or Denka butyral series manufactured by Denka Co., and includes,specifically, BH-3, BH-6, BH-A, BH-S, BX-1. BX-3, and BX-5.

Further, in the ink composition of the present invention, a phosphateester is used to easily remove dried ink coagulates at the periphery ofa ball. Particularly, while dried ink coagulates tend to be formed tothe periphery of the ball due to the resin, the coloring material andother ingredients, addition of the phosphate ester provides an effect ofmaking the dried ink coagulates easily removable. Further, the highpolymerization degree polybutyl vinylal has an effect of making the ballsurface less wetted by the internal cohesion force thereof and itcooperates with the phosphate ester.

The phosphate ester usually comprises a monoester, diester, and a minuteamount of triester of phosphoric acid and the ester structure thereof ismainly a surfactant type including two types of aromatic and aliphatictypes. For the alkyl group capable of forming the phosphate ester, alkylgroups obtained from natural and synthetic higher alcohols, etc. areintroduced. A phosphate ester having an alkyl group of 10 to 20 carbonatoms and 0 to 50 polyoxyethylene chains are used. Particularly, aphosphate ester having an alkyl group of 15 to 20 carbon atoms and from0 to 4 polyoxyethylene chains is preferred.

For neutralizing the phosphate ester, it is preferably used as a mixturewith an amine type material. As the amine type material forneutralization, it is preferred to neutralize it with an amine typecompound such as an alakanol amine, polyoxyethylene alkylamine,amphoteric surfactant and aliphatic amine type material.

For the addition amount of the phosphate ester and the amine typecompound, they are preferably added as a mixture by the neutralizationin an amount from 0.01% by weight to 15% by weight of the inkcomposition and, more preferably, it is from 0.1 to 10% by weight.Further, it is, particularly, preferably from 0.1 to 8% by weight. In acase where it is less than 0.01 by weight, ink coagulates on the surfaceof the ball and cannot be removed easily. Further, if it is blended inexcess of 15% by weight, it tends to cause disadvantages such as beingrepelled excessively from the ball tending to cause breakage of drawnlines in view of the drawing quality.

Further, in the present invention, an anti-rust agent, an anti-moldagent, a surfactant, a lubricant and a wetting agent, etc. capable ofcompatibilization with ink without giving undesired effects thereon canbe blended optionally. Particularly, a fatty acid or the like can beused suitably as the lubricant. Further, a non-volatile solvent, etc.compatible with the main solvent can also be blended, as the dryingsuppression additive, to within a range not giving undesired effects inview of the properties of the products.

In a case of using the ink composition of the present invention to aball-point pen, it is preferred to provide an ink follower to the rearend of the ball-point pen. As the solvent used is volatile, the inkfollower is added for preventing evaporation, preventing moistureabsorption and preventing ink leakage.

It is necessary for the ink follower to be less permeable and lessdiffusible to the solvent used for the ink, and non-volatile orless-volatile fluid, specifically, non-silicone type oils and fats notbasically having compatibility with the solvent described in the claimssuch as polybutene or liquid paraffin can be used as the base therefor.In a case where the viscosity of the material is low, a viscosityimprover or gelling agent is preferably used. Specifically, it includesmetal soaps, bentonites, fatty acid amides, hydrogenated castor oils,fine metal particles containing titanium oxide, silica or alumina orcelluloses and elastomers.

The reason for providing such effects resides in the feature of the inkcomposition and the blobbing phenomenon is not developed as in the usualcase by controlling the viscosity of the ink to about 10,000 mPa·s,restricting the ink discharge mechanism by the structural design such asfor the inner diameter of the ink containing tube or the clearance atthe pen tip, providing thixotropy by the addition of inorganic fillerparticles to the ink, or by the addition of a high molecular weightpolyvinyl pyrrolidone. Particularly, a high molecular weight polyvinylpyrrolidone cannot be used because the addition of the high molecularweight polyvinyl pyrrolidone to the highly hygroscopic main solventcauses violent moisture absorption under high temperature and highhumidity to remarkably increase the water content in the ink and theviscosity also lowers. As a result, sagging of an ink from the top endof the tip induces dripping of stagnated ink to a writing line, whichdeteriorates the quality of the drawn line. Further, as the watercontent continues to increase, deposition of raw materials in the inkalso occurs to result in increase of a disadvantage to the performance.As the polymer which does not cause moisture absorption as of bypolyvinyl pyrrolidone and enhances the internal cohesive force, a highpolymerization degree polyvinyl butyral is used herein. Particularly,those with a low degree of butylation in the molecule and having largeramount of hydroxyl group and higher polymerization degree tend toincrease the effect of suppressing the blobbing phenomenon. From theforegoing, it is possible to provide an oil-based ink composition foruse in a ball-point pen which restricts the development of the blobbingphenomenon remarkably by the use of the high polymerization degreepolyvinyl butyral.

<Second Aspect of the Invention (Condition (b))>

The main solvent in the solvent used for the oil-based ink compositionfor a ball-point pen in this aspect of the present invention is asolvent represented by the chemical structural formula (1):

where R¹, R², R³ each independently represents H or CH₃, and itincludes, specifically, 1,3-butanediol, 3-methoxy-1-butanol,3-methyl-3-methoxy-1-butanol, etc. By the use of the solvent describedabove, it is possible to provide a smooth writing feel. The main solventmeans 50% by weight or more based on the entire solvent and it can beused optionally by 70% by weight or more, further, 80% by weight or moreand, particularly, 90% by weight or more.

Further, as an auxiliary solvent, solvents selected from alcohols,polyhydric alcohols, glycol ethers with a vapor pressure at 25° C. of0.001 mmHg or higher are suitable.

Specific examples usable as the auxiliary solvent are identical withthose described for the first aspect.

Further, in addition to the solvents described above, polyhydric alcoholderivatives, sorbitane fatty acid type, polyglycerin higher fatty acidtype, sucrose fatty acid type, and propylene glycol fatty acid typederivatives mentioned as examples of the other solvent that can be addedwithin a range not hindering the solubility with the mixture of thephosphate ester and the amine type compound and the volatilingperformance have also been described in view of the first aspect.

The oil-based ink composition for a ball-point pen in view of the aspectof the present invention has a feature of using a pigment as a colorant.This is more excellent in view of the safety and the fastness comparedwith conventional metal-containing dyes used in oil-based ball-pointpens. The pigment may be used alone or may be used in the combined formof a pigment and a dye, particularly, in view of the coloring property.

The pigment to be used and the dye to be used in combination with thepigment can be identical to those described in view of the first aspect.

As the pigments, those less soluble in the organic solvent of thechemical structural formula (1) to be used and having an average grainsize after dispersion of from 30 nm to 700 nm are preferred. For theblending amount of the pigment, it can be blended, optionally, within arange from 0.5 to 25% by weight, preferably, from 0.5 to 20% based onthe entire amount of the ink composition.

Further, while the fastness becomes excellent by the use of the pigment,it is preferred to use the dye in combination for enhancing the coloringproperty. However, the dye to be used in combination with the pigment inthe oil-based ink composition as the second aspect of the presentinvention is preferably a dye which is stable when a 50% solution in thesolvent represented by the chemical structural formula (1) is left at 0°C. for three days and can have a viscosity of 2,000 mPa·s or lower.

By the way, it has been found that, for preparing a pigment dispersionwith the solvent comprising the solvent of the structural chemicalformula (1) as a main solvent in view of the second aspect of thepresent invention, polyvinyl butyral having a low hygroscopicity isexcellent in the stability and suitable for the pigment dispersant sincethe solvent of the chemical structural formula (1) is highlyhygroscopic. This is because the use of a highly hygroscopic polyvinylpyrrolidone, polyvinyl alcohol or polyvinyl ether may cause adisadvantage of increasing the hygroscopicity of the entire ink or causeviolent deposition of the ink to the paper surface due to the loweringof the viscosity. Other pigment dispersants, for example, styrene-maleicacid copolymer, ketone resin, hydroxyethyl cellulose or derivativesthereof, styrene-acrylic acid copolymer, etc. are not suitable sincethey tend to become unstable in the solvent to be used in view of thestability of the pigment dispersion and cause disadvantage such asoccurrence of cohesion or precipitation of the pigment. That is, in theoil-based ball-point pen ink in this aspect, only the polyvinyl butyralis used essentially as the pigment dispersant, As other resins do notcause interaction with the butyral resin, they may be used optionally.

Further, in a case of using a solvent comprising the solvent of thechemical structural formula (1) as the main solvent and providing aback-flow-preventive mechanism to the joint in the oil-based ball paintpen of the present invention, if the viscosity at 25° C. is 6,000 mPa·sor more as in conventional oil-based ball-point pens, theback-flow-preventive ball in the joint is extremely difficult to move,causing disadvantages during writing and it has been found that thepigment dispersion is necessarily giving a low viscosity. In order thatthe back-flow-preventive ball in the joint moves easily and can be usedsuitably, it has been found that the viscosity at 25° C. may be 3,000mPa·s or lower and the preferred viscosity (25° C.) is from 500 to 3,000mPa·s. In a case where it is lower than 500 mPa·s, the ink tends toblobbing to the paper surface and a sufficient performance cannot beprovided.

As described above, in order not to increase the viscosity but toenhance the dispersibility of the pigment, it has been found that theaverage molecular weight of the polyvinyl butyral is preferablyrelatively low as from 10,000 to 30,000. While not restrictive, when apolyvinyl butyral of a type having a medium or higher polymerizationdegree (average molecular weight 30,000 or more) is used as thedispersant, the dependence on the concentration increases in the organicpigment and a worry also remains in view of the stability. Further, thepigment dispersion using a dispersant of medium or higher polymerizationdegree tends to increase the viscosity excessively and it exceeds therange of the viscosity described above upon formulation into the ink.Accordingly, polyvinyl butyral with the average molecular weight up to10,000 to 30,000 is suitable.

The polyvinyl butyral used in view of this aspect of the presentinvention includes, for example, S-LEC B series manufactured by SekisuiChemical Co. and Denkabutyral series manufactured by Denka Co. and,specifically, BL-1, BL-2, BL-2H, BL-S, BL-SH, BX-10 and BX-L.

For the addition amount of the polyvinyl butyral, it is preferablydispersed by addition as the amount of the dispersant of from 20 to 60mass % based on the amount of the pigment and, it is more preferably,from 25 to 50 mass %. The pigment is used at a concentration within arange of use in view of the performance. As the concentration of thepigment increases, it may possibly exceed the predetermined range ofviscosity also in a case of formulation into the ink. On the contrary,in a case where the concentration of the pigment is excessively low, itresults in a problem for the fastness and results in trouble to lightfastness or the like.

In the oil-based ink composition in view of the second aspect of thepresent invention, while polyvinyl butyral is used for the pigmentdispersant and the fixing agent, other dispersants may also be used incombination within a range not deteriorating the purpose of the presentinvention.

As it is preferred that the back-flow-preventive ball used for theback-flow-preventive mechanism preferably has a higher specific gravityso as to be moveable easily, a metal ball, particularly, a ball made ofSUS is preferred and, further, a ball made of a super hard or carbidemetal material of further higher specific gravity is more preferred.

In the oil-based ball-point pen using the oil-based ink composition inview of the second aspect of the present invention, aback-flow-preventive mechanism is preferably provided to a joint portionconnecting a tip and an ink containing tube. As has been describedabove, in a case of using the solvent of the chemical structural formula(1) with an aim of obtaining smooth writing feel, since the disadvantagedue to intrusion of air has been found, the back-flow-preventivemechanism is provided for preventing the air intrusion.

The back-flow-preventive mechanism mounted on the oil-based ball-pointpen in view of the second aspect (effective also for the first aspect)of the present invention can be a back-flow-preventive mechanism knownin conventional aqueous ball-point pens and gel ink ball-point pens.FIG. 1 shows an example of a typical back-flow-preventive mechanism, inwhich a back-flow-preventive mechanism comprising a back-flow-preventiveball 6 and ball seats 7, 8 formed in a joint portion 5 connecting a tip1 containing a back-flow-preventive ball 2 made of a metal or a superhard (cemented carbide) material at the top end and an ink-containingtube 4 containing an ink composition 3.

The oil-based ink composition in view of the second aspect of thepresent invention is used for the oil-based ball-point pen that mountsthe back-flow-preventive mechanism and constituted such that it canprevent intrusion of air from the pen tip.

In a case of using the oil-based ink composition of the presentinvention to a ball-point pen, it is further preferred to provide an inkfollower at the rear end of the ball-point pen. As the solvent of thechemical structural formula (1) to be used is volatile, the ink followeris added for preventing evaporation, preventing moisture absorption andpreventing ink wetting. The ink follower may be those described for thefirst aspect.

Also the resin used in the oil-based ink composition for a ball-pointpen in view of this aspect of the present invention can be thosedescribed for the first aspect.

Further, in the invention, anti-rust agents, anti-mold agents,surfactants, lubricants, wetting agents, etc. that are compatible withthe ink with no undesired effect thereon can optionally be blended inthe same manner as in the first aspect.

EXAMPLES

The invention is further described specifically by way of examples butthe invention is not restricted by the examples.

<Examples for First Aspect—Condition (a))>

For the neutralization product of the phosphate ester used for thepreparation of the ink, a phosphate ester and an amine type compoundeach prepared as 2% solution of the main solvent were used andneutralizing titration was conducted to obtain a point of neutralizationof the two compounds. By mixing the two compounds at a predeterminedvalue based on the neutralization ratio, a neutralization product of thephosphate ester was obtained.

The ingredients used in the following examples and the comparativeexamples are those described below.

-   YP90L: terpenephenol resin-   Spiron Violet C-RH: spirit soluble dye based on methyl violet-   Spiron Yellow C-GNH: spirit soluble yellow dye-   Printex #35: carbon black manufactured by Degussa Co.-   Hilac 110H: alcohol soluble resin-   Spiron Blue C-RH: spirit soluble blue dye-   Chromophthal Blue-A-3R: indathrene pigment-   Chromophthal Violet B: dioxadine violet (pigment)-   Polyvinylpyrrolidone K-90: polyvinyl pyrrolidone resin

Examples 1 to 4 and Comparative Examples 1 to 4 are as shown below. Theblending amounts below are on the weight basis.

Example 1

Carbon black #25 [manufactured by Mitsubishi Kasei]   10% Polyvinylbutyral BL-S: (polymerization degree: 350,   5% theoretical molecularweight: 23,000) [manufactured by Sekisui Chemical] YP90L [manufacturedby Yasuhara Chemical]   8% Polyvinyl butyral BH-3 (polymerizationdegree: 1700,  0.5% theoretical molecular weight: 110,000) [manufacturedby Sekisui Chemical] Phosphate ester: Brisurf A208B 1.47% Amine typecompound: polyoxyethylene alkylamine 1.03% (AMIET105) 3-methoxybutanol  5% 3-methoxy, 3-methyl, 1-butanol 69.0%

Example 2

Spiron Violet C-RH   8% [manufactured by Hodogaya Chemical Industry]Spiron Yellow-C-GNH   5% [manufactured by Hodogaya Chemical Industry]Printex #35 [manufactured by Degussa Co.]   8% Polyvinyl butyral BL-1(polymerization degree: 300,   4% theoretical molecular weight: 19,000)[manufactured by Sekisui Chemical] Polyvinyl butyral BH-3(polymerization degree: 1700,  0.6% theoretical molecular weight:110,000) [manufactured by Sekisui Chemical] Hilac 110H [manufactured byHitachi Chemical]   12% Phosphate ester: Phosphanol LB-400 1.46% Aminetype compound: Polyoxyethylene oleylamine (TAMNO-5) 1.04%3-methoxybutanol  4.4% 3-methoxy, 3-methyl, 1-butanol 55.5%

Example 3

Spiron Blue C-RH   8% [manufactured by Hodogaya Chemical Industry]Spiron Violet C-RH   4% [manufactured by Hodogaya Chemical Industry]Chromophthal Blue-A-3R [manufactured by Ciba Geigy Co.]   8% Polyvinylbutyral BL-1 (polymerization degree: 300,   4% theoretical molecularamount: 19,000) [Sekisui Chemical] Polyvinyl butyral BH-S(polymerization degree: 1000,  0.5% theoretical molecular weight:66,000) [manufactured by Sekisui Chemical] Polyvinyl butyral BH-3(polymerization degree: 1700,  0.6% theoretical molecular weight:110,000) [manufactured by Sekisui Chemical] Hilac 110H [manufactured byHitachi Chemical]   8% Phosphate ester: PRISERF A208B 1.47% Amine-typecompound: polyoxyethylene alkylamine 1.03% (AMIET105) 3-methoxy,3-methyl, 1-butanol 64.4%

Example 4

Spiron Violet C-RH   10% [manufactured by Hodogaya Chemical Industry]Chromophthal Blue B [manufactured by Ciba Geigy Co.]   5% Polyvinylbutyral BL-S (polymerization degree: 350,   3% theoretical molecularamount: 23,000) [manufactured by Sekisui Chemical] Polyvinyl butyralBH-3 (polymerization degree: 1700,  0.7% theoretical molecular amount:110,000) [manufactured by Sekisui Chemical] Hilac 110H [manufactured byHitachi Chemical]   12% Phosphate ester: Phosphanol LB-400 1.46% Aminetype compound: Polyoxyethylene oleylamine 1.04% (TAMNO-5) 3-methoxy,3-methyl, 1-butanol) 66.8%

Comparative Example 1

Carbon black #25 [Mitsubishi Chemical]   10% Polyvinyl butyral BL-S(polymerization degree: 350,   5% theoretical molecular weight: 23,000)[manufactured by Sekisui Chemical] YP90L [manufactured by YasuharaChemical]   8% Phosphate ester: PRISERF A208B 1.47% Amine-type compound:polyoxyethylene alkylamine 1.03% (AMIET105) 3-methoxybutanol   5%3-methoxy, 3-methyl, 1-butanol 69.5%

Comparative Example 2

Spiron Violet C-RH   8% [manufactured by Hodogaya Chemical Industry]Spiron Yellow-C-GNH   5% [manufactured by Hodogaya Chemical Industry]Printex #35 [manufactured by Degussa Co.]   8% Polyvinyl butyral BL-1(polymerization degree: 300,   4% theoretical molecular weight: 19,000)[manufactured by Sekisui Chemical] Polyvinyl butyral BL-S(polymerization degree: 350,  0.6% theoretical molecular weight: 23,000)[manufactured by Sekisui Chemical] Hilac 110H [manufactured by HitachiChemical]   12% Phosphate ester: Phosphanol LB-400 1.46% Amine typecompound: Polyoxyethylene oleylamine 1.04% (TAMNO-5) 3-methoxybutanol 4.4% 3-methoxy, 3-methyl, 1-butanol 55.5%

Comparative Example 3

Spiron Blue-C-RH   8% [manufactured by Hodogaya Chemical Industry]Spiron Violet-C-RH   4% [manufactured by Hodogaya Chemical Industry]Chromophthal Blue-A-3R [manufactured by Ciba Geigy Co.]   8% Polyvinylbutyral BL-1 (polymerization degree: 300,   4% theoretical molecularamount: 19,000) [manufactured by Sekisui Chemical] Polyvinyl pyrrolidoneK-90 [manufactured by ISP Co.]  0.5% Hilac 110H [manufactured by HitachiChemical]   8% Phosphate ester: PRISERF A208B 1.47% Amine-type compound:polyoxyethylene alkylamine 1.03% (AMIET105) 3-methoxy, 3-methyl,1-butanol 65.0%

Comparative Example 4

Spiron Violet C-RH   10% [manufactured by Hodogaya Chemical Industry]Chromophthal Blue B [manufactured by Ciba Geigy Co.]   5% Polyvinylbutyral BL-S (polymerization degree: 350,   3% theoretical molecularamount: 23,000) [manufactured by Sekisui Chemical] Polyvinyl butyralBM-S (polymerization degree: 800,  0.7% theoretical molecular amount:53,000) [manufactured by Sekisui Chemical] Hilac 110H [manufactured byHitachi Chemical]   12% Phosphate ester: Phosphanol LB-400 1.46% Aminetype compound: Polyoxyethylene oleylamine 1.04% (TAMNO-5) 3-methoxy,3-methyl, 1-butanol 66.8%

Inks obtained in the Examples and Comparative Examples as describedabove were filled and the following evaluation tests were conducted.

1) Evaluation for Blobbing Phenomenon (Functional Evaluation):

A pen was tilted at 60° at 25° C. and 65% RH and linear writing wasconducted along a scale continuously for three times and the extent ofthe ink deposited on the pen tip was observed.

-   Fine with less ink stagnation: AA-   Some contamination with ink stagnation: BB    Remarkable contamination with much ink stagnation: CC

The ball-point pen used for the test had a polypropylene tube of 1.60 mminner diameter and a stainless steel tip (ball made of a super-hard orcarbide metal alloy of 1.0 mm diameter). Further, after filling, thefollowing evaluation was conducted after 30 min under the condition at25° C. and 65% RH.

2) Evaluation for Aged Blobbing Phenomenon Under High Humidity (SensoryEvaluation)

A pen body was left horizontally in a high temperature bath at 50° C.and 80% RH fox two weeks and, after taking out the same and leaving for1 day under the condition at 25° C. and 65% RH, the pen was set at 60°,applied with a load of 200 g and the paper in contact therewith wasmoved at a speed of 4.5 m/min and the manuscript drawn line wasobserved.

-   Fine with less ink stain to the manuscript drawn line: aa-   Relatively fine with some ink stain to the manuscript line: bb-   Not fine with much ink stain to the manuscript line: cc-   Dirty with much ink stain on the manuscript line: dd

The ball-point pen used for the test had a polypropylene tube of 1.60 mminner diameter and a stainless steel tip (ball made of a super-hardalloy of 1.0 mm diameter). Further, after filling, the followingevaluation was conducted after 30 min under the condition at 25° C. and65% RH. TABLE 1 Evaluation result Comparative Examples Examples 1 2 3 41 2 3 4 1)Evaluation AA AA AA AA CC CC CC CC 2)Evaluation aa aa aa aa cccc dd cc

As apparent from the result described above, it was found that the inkcompositions of Examples 1 to 4 within the scope of the invention wereexcellent in suppressing point seepage (deposition blobbing) of the inkto the pen tip due to manuscript and accompanying drip (drawn lineblobbing) of the ink to the paper surface as much as possible, comparedwith the ink compositions of Comparative Examples 1 to 4 that were outof the scope of the invention.

<Example for the First Aspect—Condition (b)->

Ingredients used for the following examples and comparative examples areas described below.

-   Polyvinyl butyral BL-1: polyvinyl butyral of theoretical molecular    weight of 19,000-   Polyvinyl butyral BL-S; polyvinyl butyral of theoretical molecular    weight of 23,000-   Polyvinyl butyral BM-1: polyvinyl butyral of theoretical molecular    weight of 40,000-   YP 90L: Terpene phenol resin-   Spiron violet C-RE; spirit soluble dye based on methyl violet

Spiron yellow-C-GNH: spirit soluble yellow dye

-   Printex #35: carbon black (pigment)-   Hilac 110H: alcohol soluble resin-   Chromophthal blue A-3R: Indanthrene (pigment)-   Chromophthal violet B: dioxazine violet (pigment)-   Polyvinyl pyrrolidone K-39; polyvinyl pyrrolidone resin-   Diana process oil PW-90: liquid paraffin (mineral oil)-   Aerosil R-972: fine silica particle-   P-105: terpene resin

The viscosity to be described below was measured by E-type viscometer,at EMD 10 rpm value, using a regular cone.

Examples 11 to 15 and Comparative Examples 11 to 14 are as describedbelow.

Example 11 Viscosity at 25° C.: 500 mP·s

Carbon black #25 10% [manufactured by Mitsubishi Chemical] Polyvinylbutyral BL-S  5% [manufactured by Sekisui Chemical] YP90L [manufacturedby Yasuhara Chemical] 10% 3-methoxybutanol  5% 3-methoxy, 3-methyl,1-butanol 70%

Example 12 Viscosity at 25° C.; 1100 mP·s

Spiron Violet C-RH  8% [manufactured by Hodogaya Chemical Industry]Spiron Yellow-C-GNH  5% [manufactured by Hodogaya Chemicals Insuarey]Printex #35 [manufactured by Degussa Co.]  8% Polyvinyl butyral BL-1  4%[manufactured by Sekisui Chemical] Hilac 110H [manufactured by HitachiChemical] 12% 3-methoxybutanol 10% 3-methoxy, 3-methyl, 1-butanol 53%

Example 13 Viscosity at 25° C.: 1300 mP·s

Spiron blue-C-RH 8% [manufactured by Hodogaya Chemical Industry] Spironviolet-C-RH 4% [manufactured by Hodogaya Chemical Industry] ChromophthalBlue-A-3R 8% [manufactured by Ciba Geigy Co.] Polyvinyl butyral BL-1 4%[manufactured by Sekisui Chemical] Hilac 110H [manufactured by HitachiChemical] 8% 3-methoxy, 3-methyl, 1-butanol 68%

Example 14 Viscosity at 25° C.: 1300 mP·s

Spiron violet C-RH 10% [manufactured by Hodogaya Chemical Industry]Chromophthal Blue B [manufactured by Ciba Geigy Co.] 5% Polyvinylbutyral BL-S 3% [manufactured by Sekisui Chemical] Hilac 110H[manufactured by HULUSE] 12% 3-methoxy, 3-methyl, 1-butanol 70%

Example 15 Viscosity at 25° C.: 900 mP·s

Spiron red C-GH 10% [manufactured by Hodogaya Chemical Industry] DPP RedBP [manufactured by Ciba Geigy Co.] 5% Polyvinyl butyral BL-1 3%[manufactured by Sekisui Chemical] Hilac 110H [manufactured by HitachiChemical] 12% 3-methoxy, 3-methyl, 1-butanol 70%

Comparative Example 11 With No Pigment

Spiron violet C-RH 10% [manufactured by Hodogaya Chemical Industry]Polyvinyl butyral BL-S 5% [manufactured by Sekisui Chemical] YP90L[manufactured by Yasuhara Chemical] 10% 3-methoxybutanol 5% 3-methoxy,3-methyl, 1-butanol 70%

Comparative Example 12 As Dispersant is PVP having a HighHygroscopicity, Blobbing Increases

Spiron violet C-RH 10% [manufactured by Hodogaya Chemical Industry]Chromophthal Violet B [manufactured by Ciba Geigy Co.] 5% Polyvinylpyrrolidone K-30 [manufactured by ISP Co.] 3% Hilac 110H [manufacturedby Hitachi Chemical] 12% 3-methoxy, 3-methyl, 1-butanol 70%

Comparative Example 13 Dispersant is not Dispersible Resin Other thanPVB

Spiron violet C-RH 10% [manufactured by Hodogaya Chemical Industry]Chromophthal Violet B [manufactured by Ciba Geigy Co.] 5% Hilac 110H[manufactured by Hitachi Chemical] 3% Hilac 110H [manufactured byHitachi Chemical Co.] 12% 3-methoxy, 3-methyl, 1-butanol 70%

Comparative Example 14 Not of Chemical Structural Formula (1)

Printex #35 [manufactured by Degussa Co.] 15% Polyvinyl butyral BL-1 8%[manufactured by Sekisui Chemical] Hilac 110H [manufactured by HitachiChemical] 12% Polypropylene glycol (molecular weight: 400) 40%Polypropylene glycol (molecular weight: 1000) 25%

The inks obtained in Examples and Comparative Examples described abovewere filled and the following evaluation tests were conducted.

The ball-point pen used for the tests had a polypropylene tube of 1.60mm inner diameter and a stainless steel tip (ball made of a super-hardalloy of 1.0 mm diameter). Further, after filling, the followingevaluation was conducted after 30 min under the condition at 25° C. and65% RH. The ink follower for preventing ink evaporation and preventingmoisture absorption had the following formulation. Diana process oilPW-90 67% Aerosil R-972 3% P-105 (terpene resin) 30%

As a back-flow-preventive mechanism joint, a joint for a Signo UM-100manufactured by Mitsubishi Pencil Co., was utilized and, further, joinedwith the tube using a metal tube.

1) Evaluation for Light Fastness (Mechanical Evaluation):

The pen was set at an angle of 600 at 25° C. and 65% RH and applied witha load of 200 g, and the paper in contact therewith was moved spirallyat a speed of 4.5 m/min, the manuscript line was cut out to apredetermined size and judgment was made according to the followingstandards based on the degree of discoloration at 100 h by a fade meter.

-   -   Those in which spirals could be read: AA    -   Those in which they could be read although rather pale: BB    -   Those in which they could scarcely be read: CC        2) Evaluation for Dispersion Stability;

The pigments and the dispersants were dispersed, with a formulation inwhich dyes and resins of Examples and Comparative Examples were notadded, by a paint shaker using φ0.5 zirconia beads as a media for onehour. Subsequently, each of Examples and Comparative Examples wasprepared according to the predetermined formulations. Then, afterdispersion is made, the state in which the media to as removed and theink was left at a normal temperature for 30 min was visually observed.Judgment was conducted from those showing a viscosity increase andgelation.

-   -   Those having flowability with no problem in dispersion: AA        Those somewhat poor in the flowability: BB        Those gelled and with no flowability: CC        3) Evaluation for the Ball Moveability in the        Back-Flow-Preventive Mechanism:

The pen was left pointed upwarded for three days under the condition at25° C. and 65% RH. Then, writing of circles was conducted continuouslyon predetermined writing paper and a disadvantage in view of themanuscript was observed.

-   -   Those capable of continuous writing of circles with no problem        at all: AA    -   Those not capable of transferring the ink for 1 to 2 turns to        about the third to fifth turn: BB

Those not capable of transferring the ink for 3 or more turns to aboutthe third to fifth turns: CC TABLE 2 Evaluation result ExamplesComparative Glycerin added Examples 11 12 13 14 15 11 12 13 14 Lightfastness AA AA AA AA AA CC AA — AA evaluation Dispersibility AA AA AA AAAA — BB CC BB evaluation Ball moveability AA AA AA AA AA AA AA — CCNote)Comparative Example 11: Dispersibility could not be evaluated since thepigment was not present

Comparative Example 13 It Could Not be Formulated into the Ink as thePigment Dispersion was Impossible Comparative Example 14 The Dispersionwas Evaluated as BB as the Viscosity was Excessively High Upon PigmentDispersion

As is apparent from the result described above, it was found that theink compositions of Examples 11 to 15 within the scope of the inventionwere excellent for light fastness, favorable with respect to thedispersion stability and excellent in the ensurance of theback-flow-preventive mechanism by the improvement for the movement ofthe ball compared with the ink compositions of Comparative Examples 11to 14 that are out of the scope of the invention.

INDUSTRIAL APPLICABILITY

The present invention provides an oil-based ink composition for use in aball-point pen capable of suppressing the blobbing phenomenon bycontrolling the internal cohesion of the ink, different from theexisting method, an oil based ink composition for use in ball-point penhaving smooth writing feel, excellent in the improvement of thefastness, coloring property and dispersion stability of the pigment andhaving a back-flow-preventive mechanism therein, as well as an oil-basedball-point pen using the same.

1. An oil-based ink for a ball-point pen comprising at least a colorantand a resin, as well as a solvent selected from alcohols, polyhydricalcohols and glycol ethers each having a vapor pressure at 25° C. of0.001 mmHg or higher as a main solvent occupying 50% or more of theentire solvent, and satisfying at least one of the following (a) and(b): (a) comprising from 0.01 to 1.5% by weight of a high polymerizationdegree polybutyl vinylal with a polymerization degree of 900(theoretical molecular weight of 60,000) or more, and (b) comprising apigment as the colorant and polybutyl vinylal as a dispersant, said mainsolvent being a solvent represented by the following chemical structuralformula (1)

where R¹, R², and R³ each represents independently H or CH₃.
 2. Theoil-based ink composition for a ball-point pen according to claim 1,wherein in the case of (a) described above, the glycol ether isrepresented by the following chemical structural formula (1)

where R¹, R², and R3 each represents independently H or CH₃.
 3. Theoil-based ink composition for a ball-point pen according to claim 1,wherein the colorant is a pigment or a pigment and a dye used incombination.
 4. The oil-based ink composition for a ball-point penaccording to claim 1, wherein in the case of (a) described above,polyvinyl butyral with a polymerization degree of 900 (theoreticalmolecular weight of 60,000) or less is further used as a pigmentdispersant.
 5. The oil-based ink composition for a ball-point penaccording to claim 4, wherein polyvinyl butyral with a polymerizationdegree of 200 or more and 500 or less (theoretical molecular weight offrom 10,000 to 30,000) is used as said pigment dispersant.
 6. Theoil-based ink composition for a ball-point pen according to claim 1,wherein a neutralization product of a phosphate ester is contained as anadditive.
 7. The oil-based ink composition for a ball-point penaccording to claim 1, wherein in the case of (b) described above, thepolyvinyl butyral has an average molecular weight of from 10,000 to30,000.
 8. The oil-based ink composition for a ball-point pen accordingto claim 1, which has an ink viscosity at 25° C. of from 500 to 3,000mPa·s.
 9. An oil-based ink composition for a ball-point pen comprisingat least a colorant, a resin, and from 0.01 to 1.5% by weight of a highpolymerization degree polyvinyl butyral with a polymerization degree of900 (theoretical molecular weight of 60,000) or more, and furthercomprising a solvent, as a main solvent, selected from alcohols,polyhydric alcohols and glycol ether each having a vapor pressure at 25°C. of 0.001 mmHg or higher in an amount of 50% or more based on theentire solvent.
 10. An oil-based ink composition for a ball-point pencomprising at least a pigment and a polyvinyl butyral as a dispersantand, further, comprising a solvent, as a main solvent, represented bythe following chemical structural formula (1)

where R¹, R², and R³ each represents independently H or CH₃.
 11. Anoil-based ball paint pen comprising an oil-based ink composition for aball-point pen as set forth in claim 1, and a back-flow-preventivemechanism provided to a joint portion for connecting a tip and an inkcontaining tube.
 12. The oil-based ball paint pen according to claim 11,wherein an ink follower is further provided at a rear end portion of theink composition in the ink containing tube to prevent ink evaporationand back flow.